A critical issue in mobile, portable and handheld electronics device design is space constraints. For instance, mobile phones are designed to be very small, often measuring in the neighborhood of 3″ H×2″ W×1″ D. Of that space (for instance, in an advanced clam-shell design phone that has a flip top with the screen on the inside of the top), the surface area for the physical user interface (such as numeric keys, directional toggle buttons and other controls) are required to fit in an area about 3″ H×2″ W or less. The internal space for the electronics is also exceedingly small, frequently measuring, for flip phones, less than 3″ H×2″ W×0.5″ D.
Despite those tight space constraints, the phones have more and more features, functionality and services available on them. Mobile phones have essentially become mini, mobile wireless computers. Mobile phones not only make voice calls, but they also: play games; send text messages; store address books and calendars; offer calculator functions; take, store and send photos; and play music and video clips. New features are constantly being added. This means that the user interface must advance to make all this easily accessible to the user, at the same time that the space available for more sophisticated user interfaces and internal electronics remains static or even becomes smaller.
Advances in physical user interfaces must take into account the relatively limited interface area available on mobile devices, while at the same time providing a new and advanced level of physical control for all the new features available on these devices.